pro·neph·ros 
(prō-nĕfrəs, -rŏs′)
(prō-nĕfrəs, -rŏs′)n. pl. pro·neph·roi (-roi) or pro·neph·ra (-rə)
A kidneylike organ, being either part of the most anterior pair of three pairs of organs in a vertebrate embryo, disappearing early in the embryonic development of most vertebrates.
[PRO-2 + Greek nephros, kidney.]
pro·nephric (-rĭk) adj.